1. Field of the Disclosure
The present disclosure relates to a semiconductor laser diode and method for manufacturing the same, and more particularly, to a semiconductor laser diode and method for manufacturing the same that can prevent stress concentration on a ridge portion during a flip-chip process.
2. Description of the Related Art
Since semiconductor laser diodes have a smaller size and a low threshold current lower for laser oscillation than conventional laser devices, they are widely used for high speed data transmission, recording, and reading in the field of telecommunications and in laser disc players. Particularly, nitride semiconductor laser diodes provide waves in a green to ultraviolet region, such that they are widely used for various applications such as high density optical data recording and reproducing, high-resolution laser printers, and projection TVs.
FIG. 1 shows a semiconductor laser diode disclosed in U.S. Patent Application Publication No. 2004/0174918 A1. Referring to FIG. 1, a semiconductor laser diode includes a first material layer 120, an active layer 130, and a second material layer 140 that are sequentially formed on a substrate 110. The first material layer 120 includes a buffer layer 121, a first cladding layer 122, and a first waveguide layer 123 that are sequentially formed between the substrate 110 and the active layer 130. The second material layer 140 includes a second waveguide layer 141, a second cladding layer 142, and a cap layer 143 that are sequentially formed from the active layer 130. On an upper portion of the second material layer 140, a ridge portion 151 and a protrusion portion 152 are formed. The ridge portion 151 and the protrusion portion 152 include upper portions of the second cladding layer 142 and the cap layer 143. Also, a P-type second electrode layer 171 is formed on the cap layer 143 of the ridge portion 151. The protrusion portion 152 is formed at a similar height as the ridge portion 151 to prevent stress concentration on the ridge portion 151 during a flip-chip process. Therefore, stress can be effectively distributed when the semiconductor laser diode is flip-chip bonded to a submount (heat discharge structure), such that light can be uniformly emitted over an entire ridge waveguide region. Further, a current restricting layer 160 formed of dielectric material is formed on the surfaces of the second cladding layer 142, the protrusion portion 152, and the ridge portion 151 for controlling a lateral mode. The current restricting layer 160 exposes the second electrode layer 171 formed on a top surface of the ridge portion 151. In addition, a bonding metal layer 172 is formed on surfaces of the current restricting layer 160 and the second electric layer 171, and an N-type first electrode layer 182 is formed on an exposed surface of the buffer layer 122 that has a stepped portion beside the bonding metal layer 172.
To manufacture the semiconductor laser diode having the aforementioned structure, the first material layer 120, the active layer 130, the second material layer 140, and the second electrode layer 171 are sequentially formed on the substrate 110. Next, the ridge portion 151 and the protrusion portion 152 are formed by etching, and the current restricting layer 160 is deposited entirely over the ridge portion 151 and the protrusion portion 152. Next, a top surface of the second electrode layer 171 is exposed by photolithography with a photoresist and by etching. Then, the bonding metal layer 172 is deposited.
In this manufacturing method, however, the ridge portion 151 has a narrow top width of about several micrometers. Thus, it is difficult to precisely pattern the photoresist to expose the second electrode layer 171 during the photolithography, thereby reducing process stability.
Meanwhile, if the second electrode layer 171 is exposed by planarization, the current restricting layer 160 formed on the protrusion portion 152 is also removed by over etching. Thus, the protrusion portion 152 formed of p-GaN can be exposed. FIG. 2 is an SEM photograph showing an exposed corner “A” of the protrusion portion 152 due to over etching of the current restricting layer 160 during etch-back planarization, which is performed without preparing a protective layer above the current restricting layer 160 located on the protrusion portion 152 before forming the bonding metal layer 172 on the semiconductor laser diode of FIG. 1. As a result, if the bonding metal layer 172 is formed on the exposed protrusion portion 152, the bonding metal layer 172 makes contact with the protrusion portion 152 of the second cladding layer 142 to thereby cause current leakage.